UTC (Worldtime)

Explanation

UTC, abbreviation for Universal Time Coordinated, is a
scale of time, based on the second (according to SI standard), and at the same time the primary
time zone, the worldtime, where all other time zones refer to.
It was introduced in 1926 to replace the Greenwich Mean Time (GMT).
UTC is nearly equal to the middle suntime at the meridian in Greenwich.

The german standardtime is the Middle European Time (MET), which is equal to UTC
plus 1 hour, or during daylight saving time (MEST) UTC plus 2 hours.
Therefore at computer printouts time data may be given as 14:52 UTC +1:00.

UTC runs without daylight saving time.

Greenwich Mean Time (GMT) outdated

For international and long range communications (e.g. on ships and planes) it is important not to get confused by transfering the different time zones. Therefore an agreement was met to use the time at the 0. Meridian. According to the definition, this Meridian is crossing the city Greenwich next to London and so the local time at the 0. Meridian is called the Greenwich Mean Time (GMT).

In GMT the second is defined as 1/86400 of the middle sun day (sun day = one rotation of the earth) of the actual year. But as the earth brings very varing values of rotation times and such things on their wobbly way through space, the second was not defined constantly. The daylenght is influenced by effects caused by the movement of huge masses in the liquid inner earth, tides, vulcan eruption, changes of airmass allocations and melting of ice on the poles, but even by human influences e.g. the building of dams. The friction caused by tides shortens the sun day at about 0.0016 seconds per century.

Worldtime (UT) outdated

The worldtime or universal time (UT) was introduced in 1926 to replace the Greenwich Mean Time (GMT).
It is based on astronomical observations and agrees nearly with the middle sun time at the meridian of Greenwich. Older programs and information have their time information in GMT. It is possible to replace that GMT with UTC.
Most of the astronomical calculations use UT1 - a more exact calculated form of UT. However the second of UT1 is not constant, it varies because of the different earth rotation time. That was the reason to establish a new timescale: the coordinated UT, the UTC.

Coordinated worldtime (UTC) standard

The time unit used here is the second defined by the SI system - wich is based on the atomic clock. UTC gives a highly constant time unit and agrees with the sun time. This is the reason why today UTC is the standarised base for time usage. UTC is spread out public by time transmitters and other services.
UTC has come to the base of timedata which are used international (e.g. radiostations transmitting via satelittes or short wave are using UTC, also radio operators does). Even the global navigation satellite systems use UTC to find the position all over the world. You only have to know what is the relation between UTC and your local time. Germany's local time is UTC plus 1 hour. If it is 13:00 UTC it will be 14:00 local time in germany. During daylight saving time you have to add 2 hours to the UTC time.